Although it is, perhaps, safe to assert that there is not, and never was, a Saxon vaulted church in existence; and that, during the purely Norman period, though the side-aisles of great churches were generally vaulted, the central aisle was always ceiled with wood; yet, from a study of their plans, we are led to conclude that their architects always intended that they should, or at least might, be ornamented with stone roofs. [Illustration: 810. Nave of Peterborough Cathedral.[103] (Cath. Hb.)] In the first place the area of their piers is enormous, and such as could never have been intended to support wooden roofs. Even making every allowance for the badness of the masonry, one-tenth of the sectional area would have sufficed, and not more was employed cotemporaneously in Germany when it was intended to use wooden roofs. There is also generally some variation in the design of the alternate piers, as if a hexapartite arrangement were contemplated. But the evidence is not conclusive, for the vaulting shafts are usually similar, and in all instances run from the ground through the clerestory, and terminate with the copings of the wall, so that, in their present form, they could only be meant to support the main timber of the roof. It may be that it was intended to cut them away down to the string-course of the clerestory, as was actually done at Norwich in 1446, when the nave was vaulted; but at present we must be satisfied with the evidence that the architects were content with such roofs as that of Peterborough (Woodcut No. 810), which is the oldest and finest we possess. It is very beautiful, but certainly not the class of roof these massive piers were designed to support. Though we may hesitate with regard to the intention of the builders of Norwich, Ely, or Peterborough, there can be no doubt, from the alternate piers and pillars, that when Durham (Woodcut No. 804) was commenced it was intended that the nave should be covered by a great hexapartite vault. Before, however, the intention could be carried out, the art of vaulting had been so far perfected that that very clumsy expedient was abandoned; and, by the introduction of a bracket in the nave, and afterwards of a vaulting shaft in the choir, a vault of the usual quadrilateral form was successfully carried out between the years 1233 and 1284.